BMI Calculation (Body Mass Index)

BMI is the ratio between your weight and your height squared. It's the most used indicator in the world to evaluate body size. Simple, fast, but to be interpreted with perspective.

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How is BMI calculated?

The formula is simple: BMI = weight (kg) ÷ height² (m²).

Example: 75 kg at 1.78 m → 75 ÷ (1.78 × 1.78) = 75 ÷ 3.17 = 23.7.

The World Health Organization classifies results into 4 categories: underweight (< 18.5), normal weight (18.5 – 25), overweight (25 – 30), obesity (> 30).

The limits of BMI

BMI doesn't distinguish between muscle and fat. A 100 kg rugby player who is 1.80 m tall will have a BMI of 30.9 ("obese") even though they are in great shape.

BMI doesn't take fat distribution into account. However, abdominal (visceral) fat is much more dangerous than subcutaneous fat. A waist circumference > 94 cm (men) or > 80 cm (women) is a better indicator of cardiovascular risk.

Quand consulter ?

A BMI outside the 18.5 – 25 zone doesn't necessarily mean there's a problem. But if you are over- or underweight AND feel fatigue, shortness of breath, or joint pain, it's time to see a doctor or dietitian.

BMI is a starting point, not a verdict. Combine it with other indicators (waist circumference, fat mass, physical performance) for a complete view.

Questions fréquentes

Quel est l'IMC idéal ?
The WHO considers a BMI between 18.5 and 25 to be "normal." But the ideal BMI depends on your body type, age, and muscle mass. A BMI of 22-23 is often cited as optimal for health.
L'IMC est-il fiable pour les sportifs ?
No. Muscular athletes will have a high BMI without being overweight. For them, body fat percentage (measured by bioimpedance or skinfold calipers) is a much more relevant indicator.
L'IMC est-il le même pour les hommes et les femmes ?
The formula is identical, but the interpretation can vary. Women naturally have a higher body fat percentage. A BMI of 24 doesn't mean the same thing for both genders.
À quelle fréquence recalculer son IMC ?
Every 1 to 3 months if you're in a weight loss or gain phase. Otherwise, once or twice a year is enough. BMI changes slowly.

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